1. Field of the Invention
This invention relates to a pivot assembly to be used as a bearing miniaturized and in high precision for a spindle motor to drive a disk such as a hard disk driving mechanism.
2. Conventional Art
Since recently a personal computer has been miniaturized rapidly, it is an urgent demand for miniaturizing a hard disk drive mechanism for a magnetic memory device of a computer too. Further, in a hard disk drive mechanism, in order to carry out to write in and read out information precisely, a head as a means for writing in and reading out is necessary to form a mechanism to trace a track of the disc precisely. Accordingly, a head stack assembly to carry out writing in a magnetic disk and reading out from the same is requested to be miniaturized and have a high operation precision.
FIG. 7 shows an inner structure of a hard disc drive mechanism in general. The magnetic disk D is lined up on a rotary axis C1 at a given spacing in plural number, and driven to rotate in a unitary manner by a not shown spindle motor. The head stack assembly (HSA) 1 comprises a head suspension 2 for supporting a magnetic head (not shown) on its tip end and has a structure to pivot an actuator block 3 formed with a suspension support portion 3a for supporting the head suspension 2 by the pivot assembly 4.
The pivot assembly 4 is disposed on a rotary axis C2 parallel with rotary shaft C1 and a shaft 5 is inserted at its central portion. Further, the shaft 5 comprises a sleeve 6 through a bearing. And, since the actuator block 3 is fixed to the sleeve 6, it is possible to make each head suspension 2 swing around the axis C2.
Further, although it is not shown, on an end 3b of the actuator block 3 interposing the rotary axis C2 facing to the head suspension 2, a coil is provided and a magnet is disposed by clamping the coil, which constitutes a so-called voice coil motor. By energizing the voice coil motor, the HSA 1 is swung around the rotary axis C2 to enable to make the magnetic disk D displace to the desired position of the disk D.
FIG. 8 shows the pivot assembly 4 of the HSA 1 in section. The pivot assembly 4 is formed in a unitary manner by interposing two radial ball bearings 7 and 8 between the shaft 5 and the sleeve 6. Further, between the radial ball bearings 7 and 8 an annular spacer 9 is interposed.
Two radial ball bearings 7 and 8 secure the smooth rotation between the shaft 5 and the sleeve 6 and by disposing those at a given spacing those are supported at two points in the axial direction to secure to prevent them from being deflected. Further, the spacer 9 secures the spacing between the radial ball bearing 7 and 8 and is necessary to give both a pressurization. The pressurization gives a pressure the inner ring 7a in the axial direction (lower direction in FIG. 8), and through a ball 7b, an outer ring 7c, a spacer 9, an outer ring 8c, a ball 8b and an inner ring 8a to act on a flange portion 5a of the shaft 5 to which the inner ring 8a abuts to absorb a play of the radial ball bearings 7 and 8.
As mentioned above, the pivot assembly 4 secures the rotary precision of the HSA 1 as a bearing by providing two radial ball bearings 7, 8 and the spacer 9. However, the cost of the radial ball bearings 7 and 8 which occupies the whole cost of the pivot assembly 4 has been very high and become a hindrance of the cost down. In addition, in order to prevent an unevenness of the part precision of the spacer 9 and assembling precision from influencing the rotation precision of the pivot assembly 4, cares should be taken. Further, a laminating structure of two bearing 7, 8 and the spacer 9 make the miniaturization of the pivot assembly 4 become difficult and formed a hindrance against the miniaturization of not only the HSA 1 but also the hard disk drive mechanism.
The present invention has been made in the light of the above problem, the purpose of it is to realize the miniaturization of the pivot assembly, reducing the assembling processes and lowering the cost thereof.
In order to solve the above problem, according to a first aspect of the present invention, a pivot assembly which is formed by interposing bearings between the sleeve and the shaft, a cylindrical portion of the sleeve and the shaft one bearing is disposed and on the end of the shaft a centering means for the shaft and the sleeve is provided.
In the present invention, to the bearing interposed between the cylindrical portion of the sleeve and the cylindrical surface of the shaft, a function to secure primarily the rotation of the sleeve and the shaft is made to have, and to the centering means a function primarily to prevent them from being deflected is made to have.
Further, according to a second aspect of the pivot assembly of the present invention, said centering means is adapted to become a point contact means which is interposed between the end of the shaft and the closed end of the sleeve on the central shafts of the sleeve and the shaft.
By this structure, to the centering means is adapted to have functions to prevent the sleeve and the shaft from being deflected and while allowing the rotation of the sleeve and the shaft to receive the pressurization in the axial direction of the shaft.
Further according to a third aspect of the pivot assembly of the present invention, said centering means comprises recessed portions provided on both of the closed end and the shaft end and balls to be in contact with the recessed portions. By this structure, the closed end of the sleeve and the end of the shaft are made to contact in point through the ball. This point contact is adapted to have a self centering function, since such point contact is generated by the contact between the recessed portions provided on the closed end and the shaft end and the curved surface of the surface of the ball, and said ball is guided by the recessed portion.
Further, according to a fourth aspect of the pivot assembly of the present invention, said pint contact means comprises a recessed portion provided on either one of the closed end or the shaft end and a convex portion formed on the other. By this structure, the closed end of the sleeve and the end of the shaft is made to be contacted in point through the convex portion. This point contact is adapted to have a self centering function, since such point contact is generated by the contact between the recessed portion provided on either one of the closed end and the shaft end and the convex portion of the other, the convex portion is guided by the recessed portion and has a self-centering function.
Further, according to a fifth aspect of the pivot assembly of the present invention, on the closed end coaxially with the shaft an annular projection is provided having an inner diameter a little larger than the shaft diameter. The annular projection has a function for guiding the shaft until the shaft is assembled in the sleeve and makes a point contact each other. In addition, after assembling, by applying lubricant and so on between the shaft and the annular projection the projection will also function as a guide to prevent the shaft from deflection during its rotation.
Further, according to a sixth aspect of the pivot assembly of the present invention, by forming the outer ring of the bearing in a unitary manner with the sleeve, the number of parts can be reduced and the rigidity of the sleeve can be increased due to the thickness increase of the sleeve.
In addition, according to a seventh aspect of the pivot assembly of the present invention, by forming the inner ring of the bearing in a unitary manner with the shaft, the number of parts can be reduced and the rigidity of the shaft can be increased due to the thickness increase of the shaft.